The title of the invention is Particle Guidance System. The inventor is Michael J. Renn of 9634 MacAllan Road NE, Albuquerque, N. Mex. 87109. The inventor is a citizen of the United States of America.
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The present invention relates generally to the field of optical guides. More specifically, one embodiment of the present invention relates to methods and apparatus for confining a non-atomic particle in a laser beam. The particle, which is confined in the laser beam, is guided through a hollow core optical fiber for study, measurement or deposition. The process is used to produce three-dimensional structures.
Methods for transporting atomic sized particles using radiation and pressure-based processes are known in the art, and have been used to precisely and non-mechanically manipulate particles. An atom placed in an optical beam is attracted to or repelled from regions of high intensity, depending whether the atom can be polarized at the optical frequency. Laser-induced optical forces arise when particles are polarized in intense optical fields. Laser guidance of non-atomic particles utilizes these optical forces arising generally from the deflection and scattering of light. These forces have been used in a number of optical traps. For example, xe2x80x9coptical tweezersxe2x80x9d allow dielectric particles to be trapped near the focal point of a tightly focused, high-power laser beam. These optical tweezers are used to manipulate biological particles, such as viruses, bacteria, micro-organisms, blood cells, plant cells, and chromosomes. Optical tweezers also allow a user to manipulate small, particles in an aqueous medium, though they do not allow the user to perform the same manipulation in the air. Optical traps for atoms are used in investigations of ultra-cold collisions and of the collective effects of trapped atoms.
Most known techniques for trapping atoms in a tightly focused laser beam, and for transporting atoms together with the laser beam have limitations, since the trapping occurs only in a small region near the focal point of the laser. As a result, imaging and detecting devices utilizing optical traps must be built around a sample chamber, which often limits the size of the chamber in the devices. Since trapping and transporting particles occurs inside the chamber, then these imaging and detection devices require the laser beam to be steered from outside the chamber. Moreover, optical trapping forces are typically not large enough to trap particles in the laser beam if the background medium in the chamber is turbulent or convective. Furthermore, when conventional optical tweezers are employed, only a substantially transparent particle possesses the optical qualities that are required to enable the axial force exerted on the particle in the laser beam to trap the particle inside the beam.
The technique of guiding atoms through a hollow core optical fiber was devised to improve previous procedures for manipulating particles through various media over long distances, and for transporting cold atoms from one vacuum system to another. Fiber-guided atoms are deflected from the inner surface of the fiber by light also guided in the fiber. Optical forces induced by the laser light guided in a fiber may be used to reflect atoms from the inner wall of a hollow core optical fiber. In this setting, laser light is coupled to the lowest-order grazing incidence mode, and the laser frequency is tuned to the red side. Atoms are attracted to the high intensity region at the center of the fiber. Atoms guided in a fiber this way undergo a series of loss-less oscillations in a transverse plane, and unconstrained motion in an axial direction.
While the method of guiding atoms through optical fibers was a step forward in developing means for manipulating and transporting particles from a source to a desired destination, an inherent limitation of this previous method was the atomic size of a manipulated particle. Because of an atom""s size, the wavelength of the guiding laser beam had to be close to that of an atomic transition, and the manipulation itself could be performed only in a vacuum, requiring a special vacuum chamber. The process of atomic particle transportation is limited to moving a few kinds of materials, essentially ruling out manipulating and guiding atoms of a broad range of materials. In previous nano-fabrication processes, those which guide atoms and precisely deposit them on a substrate to form nanometer size features, high throughput is not achieved.
It is desirable in industrially-applicable techniques to achieve high-rate depositions of a wide range of materials having particle sizes many times greater than single atoms. The need exists to provide a method and apparatus for manipulating and guiding microscopic (non-atomic) particles through a suitable medium along straight and bent trajectories. It is also desirable to provide a method and apparatus capable of guiding particles of a wide range of materials in non-vacuum environment and depositing the particles on various kinds and shapes of substrates.
The problem of providing a method and apparatus for optimal control of diverse material particles ranging in size from individual or groups of atoms to microscopic particles used to fabricate articles having fully dense, complex shapes has presented a major challenge to the manufacturing industry. Creating complex objects with desirable material properties, cheaply, accurately and rapidly has been a continuing problem for designers. Producing such objects with gradient or compound materials could provide manufacturers with wide-ranging commercial opportunities. Solving these problems would constitute a major technological advance, and would satisfy a long felt need in the part fabrication industry.
The present invention provides a solution to the problems encountered by previous particle manipulation methods. The present invention provides methods and apparatus for laser guidance of micron-sized and mesoscopic particles. The invention also furnishes methods and apparatus which use laser light to trap particles within the hollow region of a hollow-core optical fiber. This embodiment of the invention enables the transportation of particles along the fiber over long distances. The present invention also includes processes for guiding a wide variety of material particles, including solids and aerosol particles, along an optical fiber to a desired destination.
The present invention further includes methods and apparatus for guiding particles in ambient, aqueous or gaseous environments, including an inert gas environment, which may be desirable for the fabrication of objects.
The invention may also be employed to deliver liquid and solid particles to a substrate using a laser to guide particles in hollow-core optical fibers after extracting the particles from source backgrounds. This method allows a user to fabricate micron-size surface structures, such as electrical circuits and micro-electronic-mechanical devices, on a virtually unlimited variety of substrates, including semiconductors, plastics, metals and alloys, ceramics and glasses. The particles deposited on such substrates can be metals or alloys, semiconductors, plastics, glasses, liquid chemical droplets and liquid droplets containing dissolved materials or colloidal particles.
Another embodiment of the invention may be used as a fiber optic particle guide for non-contact, non-mechanical manipulation of mesoscopic particles. Such particles include those of biological origin such as bacteria, viruses, genes, proteins, living cells and DNA macromolecules. The particles can also be inorganic, such as glasses, polymers and liquid droplets.
Another embodiment of the present invention provides a method of controlling and manipulating non-atomic particles by trapping them within an optical fiber anywhere along the length of the fiber. A laser beam may be directed to an entrance of a hollow-core optical fiber by a focusing lens. A source of particles to be guided through the fiber provides a certain number of particles near the entrance to the fiber. The particles are then drawn into the hollow core of the fiber by the focused laser beam, propagating along a grazing incidence path inside the fiber. Laser induced optical forces, generated by scattering, absorption and refraction of the laser light by a particle, trap the particle close to the center of the fiber and propels it along. Virtually any micron-size material, including solid dielectric, semiconductor and solid particles as well as liquid solvent droplets, can be trapped in laser beams, and transported along optical fibers due to the net effect of exertion of these optical forces. After traveling through the length of the fiber, the particles can be either deposited on a desired substrate or in an analytical chamber, or subjected to other processes depending on the goal of a particular application.
In another embodiment of the present invention, the particle manipulation methods are used to levitate particles inside a hollow-core fiber. In this method, particles or liquid droplets captured by a tightly focused laser beam are drawn into a vertically positioned fiber. After a certain distance inside the fiber, the propelling axial optical force pulling the particle up is balanced by the gravitational force acting on the particle. Such a balance of forces makes the particle levitate in an equilibrium position, allowing the estimation of the magnitude of the propelling force. Similarly, if a particle is trapped in a horizontally positioned optical fiber by two laser beams entering the fiber from two opposing ends of the fiber, the particle will levitate in a certain equilibrium position inside the fiber. Varying the intensity of the lasers allows one to estimate the magnitude of the force confining the particle in the center of the fiber.
The invention may also be utilized to transport and pattern aerosol particles on a substrate. By directing particles along the fiber and onto the substrate, micron-size features of desirable shape can be fabricated by directed material deposition (DMD) of these particles. Such features are built up by continual addition of particles, which are fused together on the substrate by various techniques including xe2x80x9cin-flightxe2x80x9d melting of the particles and subsequent coalescence of molten droplets on the substrate. This embodiment also offers the ability to simultaneously deposit solid particles and liquid xe2x80x9cprecursors,xe2x80x9d where the liquids serve to fill the gaps between solid particles. A precursor is any material that can be decomposed thermally or chemically to yield a desired final product. Coalescence of liquid precursors on the substrate and subsequent decomposition by laser heating to form a final product on the substrate and sintering of the deposited material by laser, or chemical binding are additional techniques made possible by the invention. Another technique that is enabled by the invention is the heating of a substrate, as in conventional CVD processes.